1. Field of the Invention
The present invention relates to a capacitor-mounted metal foil and a circuit board using the same, and a method for producing them.
2. Description of the Related Art
In recent years, with the demand for high performance and miniaturization of electronic equipment, there is an increasing demand for high density and high function of a semiconductor device. This results in a demand for a miniaturized high-density circuit board for mounting a semiconductor device.
Furthermore, when semiconductor devices are mounted at high density, heat and noise are generated by components. Thus, in order to mount semiconductor devices at high density, a circuit board is required that allows high-density mounting and is excellent in a thermal dissipation property and noise resistance.
As a technique of improving the thermal dissipation property of a circuit board, a heat-conductive substrate using a thermosetting resin and an inorganic filler has been proposed (see JP 10-173097 A). Furthermore, JP 11-168112 A has proposed a method for heating and pressurizing a sheet-shaped material containing a mixture of an inorganic filler and a thermosetting resin, thereby performing mounting and sealing of semiconductor devices simultaneously.
As a general method for enhancing the noise resistance of a circuit board, capacitors for removing noise are mounted on a circuit board so as to absorb high-frequency noise and ripple. However, in the case where capacitors are mounted on a circuit board, the size of the circuit board is enlarged so as to ensure a mounting area for the capacitors. Therefore, there has been an attempt in which capacitors are embedded in a circuit board.
For example, methods for forming a capacitor in a ceramic substrate have been proposed (JP 62-131411 A, JP 1-152688 A, and JP 2-305490 A). According to these methods, a ceramic substrate material and a ceramic dielectric material capable of being sintered under the same conditions as those of the substrate material are layered on one another, and both the materials are sintered simultaneously, whereby capacitors are formed in a ceramic substrate.
However, a conventional ceramic substrate with capacitors embedded therein entails a high cost. Furthermore, it takes a long period of time to produce a prototype of and to change the design of such a substrate. On the other hand, according to the method for embedding ceramic capacitors made of a sintered body in an inexpensive resin substrate, the sintered body may be broken when the substrate is layered to form a multi-layer structure.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a capacitor-mounted metal foil, which allows high-density mounting and allows an inexpensive circuit board excellent in noise resistance and a thermal dissipation property to be formed, and a method for producing the same. It is another object of the present invention to provide an inexpensive circuit board, which allows high-density mounting and is excellent in noise resistance and a thermal dissipation property, and a method for producing the same.
In order to achieve the above-mentioned object, the capacitor-mounted metal foil of the present invention is provided with a metal foil and a plurality of capacitors formed on the metal foil, and each of the capacitors includes: a conductive layer disposed above the metal foil; and a dielectric layer disposed between the metal foil and the conductive layer. Since the above-mentioned capacitor-mounted metal foil includes capacitors, a circuit board excellent in noise resistance can be produced. Furthermore, the capacitor-mounted metal foil is flexible, so that a circuit board can be produced using a resin. Also, an inexpensive circuit board can be produced, which allows high-density mounting and is excellent in a thermal dissipation property.
In the present specification, the term xe2x80x9cmetal foilxe2x80x9d refers to a film, a layer, a sheet, and the like. Furthermore, in the present specification, for easy understanding, the terms xe2x80x9cmetal foilxe2x80x9d and xe2x80x9cmetal filmxe2x80x9d are used for another member; however, there is no difference in meaning therebetween.
In the above-mentioned capacitor-mounted metal foil, the capacitor further may include a metal layer disposed between the metal foil and the dielectric layer, and a surface of the metal layer that is in contact with the dielectric layer may be roughened. According to this structure, a capacitor with a large capacitance can be formed. Furthermore, by controlling the degree of roughness, the capacitance of a capacitor can be regulated.
In the above-mentioned capacitor-mounted metal foil, the dielectric layer may be made of an oxide of the metal forming the metal layer. According to this structure, production becomes easy.
In the above-mentioned capacitor-mounted metal foil, the metal layer may be made of a material selected from the group consisting of aluminum, tantalum, and niobium. According to this structure, an aluminum electrolytic capacitor and a tantalum electrolytic capacitor can be formed.
In the above-mentioned capacitor-mounted metal foil, the metal foil and the metal layer may be bonded to each other via a metallic bond. According to this structure, a capacitor-mounted metal foil can be produced, which enables a highly reliable circuit board to be produced.
In the above-mentioned capacitor-mounted metal foil, a thickness of the metal layer may be in a range of 10 xcexcm to 100 xcexcm. By prescribing the thickness of the metal layer to be 10 xcexcm or more, the surface of the metal layer can be roughened easily.
In the above-mentioned capacitor-mounted metal foil, the metal foil may be made of a material selected from the group consisting of copper and nickel. According to this structure, a wiring pattern that is soldered easily at a low resistance can be formed.
In the above-mentioned capacitor-mounted metal foil, a thickness of the metal foil may be in a range of 3 xcexcm to 70 xcexcm. It is preferable that the thickness of the metal foil is in a range of about 3 xcexcm to about 18 xcexcm for forming a fine wiring pattern. It is preferable that the thickness of the metal foil is 18 xcexcm or more for mounting a component by soldering. Furthermore, it is preferable that the thickness of the metal foil is in a range of about 35 xcexcm to about 70 xcexcm for forming a wiring pattern through which a large current flows. Furthermore, it is preferable that the thickness of the metal foil is in a range of about 18 xcexcm to about 70 xcexcm for facilitating handling. Furthermore, it is preferable that the metal foil is thinner for producing a thin circuit board.
In the above-mentioned capacitor-mounted metal foil, the conductive layer may include a conductive polymer layer and an electrode made of metal that are layered successively from the metal foil side. According to this structure, a capacitor having a small equivalent series resistance (hereinafter, it may be referred to as an xe2x80x9cESRxe2x80x9d) can be produced.
In the above-mentioned capacitor-mounted metal foil, the electrode may be made of at least one metal selected from the group consisting of silver, copper, nickel, and aluminum. According to this structure, since an Ohmic contact can be formed, a capacitor having a small ESR can be produced.
In the above-mentioned capacitor-mounted metal foil, the conductive layer may include a conductive polymer layer and a carbon layer that are layered successively from the metal foil side. According to this structure, since an Ohmic contact can be formed, a capacitor having a particularly small ESR can be produced.
In the above-mentioned capacitor-mounted metal foil, the dielectric layer may be made of a nonconductive polymer. The nonconductive polymer has a low dielectric constant; however, it is easily handled due to its high mechanical strength and is unlikely to be damaged during layering on a substrate.
The above-mentioned capacitor-mounted metal foil further may include a resistor formed on the metal foil. According to this structure, resistors as well as capacitors can be embedded in a circuit board, so that higher density of the circuit board can be obtained.
In the above-mentioned capacitor-mounted metal foil, the plurality of capacitors may be arranged in a grid array shape on the metal foil. According to this structure, flip chip bonding in which a semiconductor is mounted directly can be utilized, whereby a capacitor can be formed immediately under a semiconductor. In addition, a capacitor can be formed immediately under a lead electrode of a chip size package. This will stabilize noise and a power supply voltage.
The above-mentioned capacitor-mounted metal foil may include an insulating polymer layer on a part of the metal foil where no capacitors are formed. According to this structure, the metal foil can be prevented from being damaged during etching or oxidation. Furthermore, by prescribing the height of the insulating polymer layer to be substantially equal to that of the capacitor, mechanical stress can be prevented from being concentrated on the capacitor during pressing and heating of a circuit board. Furthermore, in producing a circuit board, the insulating polymer layer can be used as an adhesive layer.
Furthermore, the circuit board of the present invention includes: an insulating base; a plurality of wiring patterns formed on at least two principal planes of the base; inner vias formed in the base so as to connect the plurality of wiring patterns to each other; and a plurality of capacitors formed on a surface of at least one wiring pattern selected from the plurality of wiring patters, wherein each of the capacitors includes a conductive layer disposed above the at least one wiring pattern and a dielectric layer disposed between the at least one wiring pattern and the conductive layer. This circuit board allows high-density mounting, and is inexpensive and excellent in noise resistance and a thermal dissipation property. In particular, in this circuit board, the capacitors are connected to the wiring patterns through the inner vias, which is very effective for reduction of noise in a high-frequency circuit, and high-density mounting of circuit components. Furthermore, in the circuit board, the capacitors can be connected in the thickness direction of the board, so that an ESL (Equivalent Series Inductance) can be decreased. In the present specification, the phrase xe2x80x9cto connect the plurality of wiring patterns to each otherxe2x80x9d also indicates an indirect connection via the capacitors.
In the above-mentioned circuit board, the plurality of wiring patterns may include a wiring pattern formed in the base. According to this structure, a circuit board is obtained in which wiring patterns are formed in multi-layers. This allows miniaturized high-density mounting with a high degree of freedom of wiring pattern.
In the above-mentioned circuit board, the capacitor further may include a metal layer disposed between the at least one wiring pattern and the dielectric layer, and a surface of the metal layer that is in contact with the dielectric layer may be roughened.
In the above-mentioned circuit board, the dielectric layer may be made of an oxide of the metal forming the metal layer.
In the above-mentioned circuit board, the metal layer may be made of a material selected from the group consisting of aluminum, tantalum, and niobium.
In the above-mentioned circuit board, the at least one wiring pattern and the metal layer may be bonded to each other via a metallic bond.
In the above-mentioned circuit board, the at least one wiring pattern may be made of a material selected from the group consisting of copper and nickel.
In the above-mentioned circuit board, the conductive layer may include a conductive polymer layer and an electrode made of metal that are layered successively from the at least one wiring pattern side.
In the above-mentioned circuit board, the electrode may be made of at least one metal selected from the group consisting of silver, copper, nickel, and aluminum.
In the above-mentioned circuit board, the conductive layer may include a conductive polymer layer and a carbon layer that are layered successively from the at least one wiring pattern side.
In the above-mentioned circuit board, the dielectric layer may be made of a nonconductive polymer.
The above-mentioned circuit board further may include a resistor disposed between wires of the at least one wiring pattern.
In the above-mentioned circuit board, the plurality of capacitors may be arranged in a grid array shape on the at least one wiring pattern. According to this structure, a power supply circuit and a signal circuit that require capacitors can be connected easily.
In the above-mentioned circuit board, all of the plurality of capacitors may be connected to the inner vias.
In the above-mentioned circuit board, the base may include a thermosetting resin and an inorganic filler. According to this structure, a circuit board having a high thermal dissipation property can be obtained. Furthermore, according to this structure, physical properties of the base can be made uniform, so that a highly reliable circuit board can be obtained.
In the above-mentioned circuit board, the base may include a thermosetting resin and reinforce. According to this structure, conventionally used materials for a circuit board can be used.
Furthermore, the method for producing a capacitor-mounted metal foil of the present invention is a method for producing a capacitor-mounted metal foil provided with a metal foil and a plurality of capacitors formed on the metal foil, including: (a) forming a metal layer disposed on a part of the metal foil and a dielectric layer disposed on the metal layer; and (b) forming a conductive layer on the dielectric layer. According to this production method, the capacitor-mounted metal foil of the present invention can be produced easily.
In the above-mentioned method for producing a capacitor-mounted metal foil, the dielectric layer may be made of an oxide of the metal forming the metal layer. According to this structure, the capacitor-mounted metal foil of the present invention can be produced easily.
In the above-mentioned method for producing a capacitor-mounted metal foil, the process (a) may include: (a-1) forming a metal film on the metal foil; (a-2) roughening a surface of a part of the metal film; (a-3) oxidizing the roughened surface of the metal film to form the metal layer and the dielectric layer; and removing a part of the metal film after the process (a-1). According to this structure, a capacitor with a large capacitance can be produced easily.
In the above-mentioned method for producing a capacitor-mounted metal foil, the process (a-1) may be conducted by hot rolling or cold rolling, and the metal foil and the metal film may be bonded to each other via a metallic bond.
In the above-mentioned method for producing a capacitor-mounted metal foil, the process (a-2) may be conducted by at least one method selected from the group consisting of chemical etching, electrochemical etching, and sandblasting. According to this structure, the surface of the metal film can be roughened easily.
In the above-mentioned method for producing a capacitor-mounted metal foil, in the process (a-3), the surface of the metal film may be oxidized by anodization. According to this structure, a uniform and stable oxide layer can be formed.
In the above-mentioned method for producing a capacitor-mounted metal foil, the metal film may be made of a material selected from the group consisting of aluminum, tantalum, and niobium.
In the above-mentioned method for producing a capacitor-mounted metal foil, the metal foil may be made of a material selected from the group consisting of copper and nickel.
In the above-mentioned method for producing a capacitor-mounted metal foil, the process (a) may include forming an insulating polymer layer on a part of the metal foil where the metal layer is not formed.
In the above-mentioned method for producing a capacitor-mounted metal foil, the process (a) may include forming a metal layer on a part of the metal foil, and forming the dielectric layer made of a nonconductive polymer on the metal layer.
In the above-mentioned method for producing a capacitor-mounted metal foil, the conductive layer may include a conductive polymer layer and an electrode made of metal successively layered from the metal foil side.
The above-mentioned method for producing a capacitor-mounted metal foil further may include forming a resistor connected to the metal layer.
Furthermore, the method for producing a circuit board of the present invention is a method for producing a capacitor-embedded circuit board, including: (i) forming capacitors on a metal foil; (ii) laminating a prepreg in which inner vias are formed and the metal foil on each other so that the capacitors are embedded in the prepreg; (iii) curing the prepreg; and (iv) removing a part of the metal foil to form a wiring pattern, wherein the process (i) includes (a) forming a metal layer disposed on a part of the metal foil and a dielectric layer disposed on the metal layer and (b) forming a conductive layer on the dielectric layer. According to this method for producing a circuit board, the circuit board of the present invention can be produced easily.
In the above-mentioned method for producing a circuit board, the dielectric layer may be made of an oxide of the metal forming the metal layer.
In the above-mentioned method for producing a circuit board, the process (a) may include: (a-1) forming a metal film on the metal foil; (a-2) roughening a surface of a part of the metal film; (a-3) oxidizing the roughened surface of the metal film, thereby forming the metal layer and the dielectric layer; and removing a part of the metal film after the process (a-1).
In the above-mentioned method for producing a circuit board, the metal film may be made of a material selected from the group consisting of aluminum, tantalum, and niobium.
In the above-mentioned method for producing a circuit board, the metal foil may be made of a material selected from the group consisting of copper and nickel.
In the above-mentioned method for producing a circuit board, the prepreg may include a metal film on a surface opposite to a surface that is in contact with the metal foil, and the process (iii) may include curing the prepreg, and electrically connecting the capacitors to the metal film.
The above-mentioned method for producing a circuit board further may include forming a wiring pattern on a surface of the prepreg after the process (iii).
The above-mentioned method for producing a circuit board may include layering the metal foil, on which the capacitors are formed in the process (i), and the prepreg on the base obtained in the process (iv) to form a multi-layer board. According to this structure a circuit board provided with multi-layer wiring patterns can be produced.
In the above-mentioned method for producing a circuit board, the inner vias may be formed by filling through-holes in the prepreg with a conductive paste. According to this structure, when the capacitors are embedded in the prepreg, the dielectric layer can be prevented from being damaged.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.